gr-qc — Pith

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gr-qc 2026-05-13 2 theorems

Cotton gravity forces Cotton-φ-perfect fluid structure on static spatial slices

The spatial Riemannian factor obeys this generalized perfect fluid condition, reducing to the standard case under extra assumptions.

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We analyze the geometry of the field equations of Cotton gravity (for a quite general energy-momentum tensor) on a static space-time. In particular, we describe the local structure of the spatial Riemannian factor. This structure, that we call Cotton-$\varphi$-perfect fluid (C-$\varphi$-PF, for short) is a generalization to the regime of Cotton Gravity of the recently introduced notion of $\varphi$-static perfect fluid space-time ($\varphi$-SPFST). After discussing the variational origin of this system, we provide sufficient conditions for a C-$\varphi$-PF to reduce to a $\varphi$-SPFST. We also study the geometry of the level sets of the lapse function $f$ and we provide a rigidity result for C-$\varphi$-PFs under some curvature conditions. The role that Codazzi tensors hold in this theory is highlighted.

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gr-qc 2026-05-13 1 theorem

CBC background cuts ET CW sensitivity 7-10% near 7 Hz

Impact of coalescence signals on the search for continuous gravitational waves with Einstein Telescope

Simulations show unresolved coalescences add noise that hits the Frequency-Hough search hardest at low frequencies.

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The current network of gravitational wave detectors has already revealed hundreds of compact binary coalescences (CBCs), including binary neutron stars, binary black holes, and black hole-neutron star systems. As detector sensitivity improves, the superposition of these signals is expected to form an astrophysical background that becomes increasingly relevant for future observatories. In third generation detectors, such as the Einstein Telescope (ET), this background will be most prominent at low frequencies, potentially affecting the search for continuous gravitational waves (CWs) from spinning neutron stars. In this work, we evaluate the impact of the CBC background on CW detection using the Frequency-Hough pipeline, with a focus on the low-frequency performance in ET sensitivity conditions. Through realistic simulations of the unresolved CBC background, we find that it acts as an additional noise source, most strongly affecting the detection of CW signals around 7 Hz, worsening the FH sensitivity by about 7-10%.

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gr-qc 2026-05-13 3 theorems

Deformations tune Mixmaster epoch lengths

Chaos and epoch structure in the deformed Mixmaster universe

GUP shortens Kasner epochs and raises collision rates while polymerization lengthens them and suppresses bounces.

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We study the dynamics of the Bianchi~IX (Mixmaster) universe under classical polymerization and generalized uncertainty principle (GUP) deformation of the Poisson brackets. Starting from the Misner Hamiltonian, we derive the effective equations of motion with both modifications and analyze the duration of Kasner epochs as a probe of dynamical behavior. Our results show that GUP corrections typically shorten the epochs, leading to more frequent wall collisions, whereas polymer corrections prolong them and suppress successive bounces. At leading order, the combined deformation produces an additive shift that interpolates between these two trends. While the billiard picture remains robust, the strength of Mixmaster chaos becomes sensitive to the deformation parameters. These results illustrate how Planck-scale corrections may either enhance or suppress cosmological chaos, offering a controlled framework for exploring early-universe dynamics.

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gr-qc 2026-05-13 Recognition

Proca hair reduces damping in scalar modes of de Sitter black holes

Quasinormal Spectra of Fields of Various Spin in Asymptotically de Sitter Black Holes within Generalized Proca Theory

The ℓ=0 scalar sector is most sensitive, with weaker damping as the three-horizon regime approaches, while β hardens and λ, c1 soften the

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We study massless scalar, electromagnetic, and Dirac perturbations of asymptotically de Sitter black holes in generalized Proca theory. These geometries are especially interesting because the Proca sector generates both a primary-hair parameter and an effective cosmological term $\Lambda_{\rm eff}$, thereby reshaping the horizon structure and the size of the static patch. Working on this common hairy background, we derive the master equations for the three spin sectors and analyze their quasinormal spectra by means of Pad\'e-improved WKB calculations supplemented by characteristic time-domain integration. We show that the scalar sector, especially the $\ell=0$ mode, is the most sensitive to metric deformations; increasing the Proca-hair parameter $Q$ weakens the damping as the charged three-horizon regime is approached; $\beta$ hardens the spectrum in the $(\alpha,\beta)$ scan; and increasing $\lambda$ and $c_1$ produces the strongest overall softening. For the neutral scalar $\ell=1$ mode, the time-domain Prony extraction agrees excellently with the WKB results and resolves both the Schwarzschild-like black-hole branch and the de Sitter branch. We also discuss the implications of the exact empty-de Sitter limit for strong cosmic censorship and note that the resulting quasinormal frequencies provide useful input for grey-body factors.

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gr-qc 2026-05-13 2 theorems

Gödel metrics solve curvature-squared gravity with CTCs allowed

Causality Violating Solutions in Curvature-Squared Gravity

Weyl tensor terms vanish in these solutions but modify energy density for axially symmetric cases.

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In this paper, we consider some causality violating solutions in the curvature-squared gravity in order to examine whether closed timelike curves (CTCs) are allowed in these models. These aspects are studied in terms of the G\"odel, G\"odel-type and axially symmetric cosmological solutions. We observe that the G\"odel and G\"odel-type metrics are causal solutions of the model so that CTCs are now allowed and, surprisingly, every contribution involving the Weyl tensor is removed from the solutions. Hence, in order to study the effect (if any) of the Weyl tensor (an conformal symmetry) into CTCs a third metric is considered. In this case, we obtain contributions due to the Weyl tensor to the energy density and led to modifications of the weak energy condition.

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gr-qc 2026-05-13 2 theorems

Generalized horizon entropy derives Friedmann equation

Generalized Mass-to-Horizon Entropy and Horizon Thermodynamics

A two-parameter extension of Bekenstein entropy accounts for all heat exchange and confirms the universe evolves to stable maximum entropy.

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We investigate the cosmological implications of generalized mass-to-horizon entropy, a two-parameter extension of the standard Bekenstein entropy based on the mass-to-horizon relation. Assuming the entropy balance relation, we derive the change in the generalized mass-to-horizon entropy, which entirely accounts for the heat exchange across the horizon as measured by an observer near the apparent horizon. We have then derived the Friedmann equation, using the Clausius relation, and also using modified law of thermodynamics. The thermodynamic consistency of the entropy, is examined through entropy evolution and entropy maximization conditions, where the generalized entropy and its higher-order derivatives indicate that the universe evolves toward a stable maximum entropy configuration consistent with the generalized second law of thermodynamics. In addition, fluctuations in horizon energy are investigated to probe the thermal stability and thermodynamic behavior of the cosmic horizon. The fluctuation analysis reveals finite and physically stable behavior throughout cosmic evolution, supporting the thermodynamic viability of the proposed model. The present work therefore establishes the generalized mass-to-horizon entropy as a viable thermodynamic framework for describing modified cosmological dynamics and also the accelerated expansion of the universe as well.

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gr-qc 2026-05-13 2 theorems

Variable choice decides what the Friedmann equations reveal

The choice of variables in cosmological dynamical systems

Different normalizations of the same cosmological system can expose or conceal fixed points and their stability properties.

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Dynamical systems techniques are a powerful tool to analyse systems of ordinary differential equations, written in an appropriate form. For a given theory of gravity, the cosmological field equations typically lead to a system of ordinary differential equations. Casting these cosmological equations into the form of a dynamical system requires a careful choice of the dynamical variables. Despite this being a critical step, relatively little is said about this process in the literature. We discuss how different variable choices affect the information that can be extracted from the Friedmann equations. We begin by reviewing the standard cosmological model with dark matter, radiation, and dark energy, and include quintessence models. We revisit well-known models with an exponential potential using new variables. This discussion is then extended to models with scalar fields and more intricate coupling terms.

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gr-qc 2026-05-13 2 theorems

Cosmology drives tensor-speed changes below ringdown reach

A cosmology-to-ringdown EFT consistency map for scalar-tensor gravity

A new EFT bridge shows inherited modifications vanish for black-hole vibrations while strong-field operators that average out in the early

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We construct an effective-field-theory bridge from late-time scalar-tensor cosmology to black-hole ringdown observables. Starting from a cosmology-conditioned EFT posterior, we lift Jordan-frame FLRW data through a finite covariant jet, transport the result to the arbitrary-background EFT for black-hole perturbations with a timelike scalar, and project it onto parity-resolved quasinormal-mode response kernels. The cosmological layer is a deterministic compressed likelihood built from BAO-like distances, growth summaries, low-redshift tensor-speed information, stability filters, and posterior samples for the ringdown pushforward. The detector layer uses Bayesian time-domain injections, one-, two-, and three-mode recovery models, analytic marginalization over linear sine/cosine amplitudes, remnant-calibration covariance products, and start-time variations. The transported posterior shows that FLRW tensor-speed deformations inherited from cosmology are driven far below ringdown detectability, whereas operators that vanish on homogeneous FLRW backgrounds can remain active in the anisotropic near zone of a black hole. For a literature-calibrated Hayward branch, we specify the prior measure, separate directly admissible points from a proxy continuation, and propagate both to detector-whitened consistency modes. The resulting framework turns cosmological viability into black-hole spectroscopy priors while keeping the strong-field completion explicit rather than assumed.

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gr-qc 2026-05-13 2 theorems

Codazzi tensor corrects entropy in Cotton gravity horizons

Thermodynamic formulation of Cotton gravity in the Codazzi parametrization

First law on apparent horizons adds a term whose sign can identify the matter content.

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We develop a thermodynamic formulation of Cotton gravity in the Codazzi parametrization, providing a general framework in which the gravitational dynamics can be interpreted in terms of horizon thermodynamics. As paradigmatic examples, we apply the formalism to FriedmannRobertson-Walker (FRW) and static spherically symmetric spacetimes. By implementing the first law of thermodynamics on the apparent cosmological and event horizons, we derive a modified holographic entropy consisting of the standard Bekenstein-Hawking term supplemented by a correction induced by the Codazzi tensor. In the cosmological setting, this correction is governed by the temporal component of the Codazzi tensor, while in static configurations it is controlled by its anisotropic sector. Remarkably, the sign of this contribution provides a potential diagnostic of the underlying matter content, allowing one to distinguish between ordinary matter, a cosmological constant and phantom-like components. These results establish horizon thermodynamics as a sensitive probe of Cotton gravity, offering a complementary perspective beyond background kinematics and enabling a characterization of the statistical and thermodynamic properties of spacetime within the Codazzi formulation.

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gr-qc 2026-05-13 2 theorems

Black hole mergers calibrate gravitational wave detectors

GW240925 and GW250207: Astrophysical Calibration of Gravitational-wave Detectors

Two loud binary black hole events yield the first direct astrophysical constraints on LIGO and Virgo calibration uncertainties.

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GW240925 and GW250207 are two loud gravitational-wave signals from binary black hole coalescences observed with network signal-to-noise ratios $\sim 32$ and $\sim 69$, respectively, by the LIGO Hanford--LIGO Livingston--Virgo network. Gravitational-wave signals from coalescing binaries have characteristic phase and amplitude evolution predicted by general relativity. These signal waveforms, together with measured instrumental calibration uncertainties, are used to infer source parameters. However, for sufficiently loud detections it is possible to constrain the calibration of the detectors directly using the signals themselves. We present the first informative astrophysical measurements of gravitational-wave detector calibration. For GW240925, we verify the inference of Hanford calibration from the astrophysical signal through cross-checks with known calibration errors obtained from in-situ measurements. At the time of GW250207, the Hanford detector was not fully stabilized, leading to elevated calibration uncertainties; thus, astrophysical calibration is essential to obtain accurate data and to enable source localization. These well-localized, high signal-to-noise observations have the potential to offer precise measurements of source properties, stringent tests of general relativity, and informative dark siren measurements, provided that calibration uncertainties are properly incorporated. As detector sensitivity improves, astrophysical calibration will become an increasingly valuable complement to in-situ calibration measurements. Obtaining accurate calibration will be essential for precision gravitational-wave science.

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gr-qc 2026-05-13 2 theorems

One f(Q,L_m) function drives both inflation and late acceleration

Cosmology of f(Q,L_m) gravity with Holographic Ricci Dark Energy: Early-Time Inflation and Late-Time Acceleration and RGUP Corrected Observables

Quadratic term produces Starobinsky-like early phase; remaining terms plus holographic dark energy handle late expansion with only small RGU

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This study investigates a cosmological scenario within the f(Q,L_m) gravity framework to explore whether one geometric model can simultaneously describe the early and late-time accelerated epochs. Motivated by the recently proposed f(Q,L_m) gravity framework by Hazarika et al. [Phys. Dark Universe 50 (2025) 102092], we adopt a minimal polynomial form, f(Q,L_m) = -Q + alpha Q^2 + 2L_m + beta QL_m, and the late-time dynamics are reconstructed by introducing Holographic Ricci Dark Energy (HRDE) as an effective fluid. The resulting background evolution demonstrates smooth accelerated expansion, stable Hubble parameter behavior, and an effective equation of state that approaches the de Sitter regime. Bayesian analysis utilizing Pantheon supernovae, cosmic chronometer, and DESI BAO data reveals that the matter-geometry coupling parameter beta is weakly constrained and remains consistent with the LambdaCDM limit. In the high-curvature regime characteristic of the early Universe, the quadratic non-metricity term alpha Q^2 dominates the dynamics, resulting in a Starobinsky-like inflationary phase driven solely by geometric effects with predicted n_s and r values consistent with Planck 2018 observations. Furthermore, quantum-gravity-inspired corrections are examined through a Relativistic Generalized Uncertainty Principle (RGUP), implemented as a momentum-dependent deformation of the effective spacetime metric. These corrections maintain the geometric inflationary background while introducing minor perturbative shifts in higher-order inflationary observables, specifically the running of the spectral index. Overall, these findings indicate that the f(Q,L_m) framework offers a dynamically consistent geometric model in which early and late cosmic acceleration arise from distinct curvature regimes, with RGUP effects causing sub-leading modifications.

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gr-qc 2026-05-13 2 theorems

SNAIL circuits host stable analogue black-white holes

Stability and quasi-normal ringing in analogue black-white holes in SNAIL-based traveling-wave parametric amplifiers

No negative modes and first QNM calculation show ringdown timescales before nonlinear dispersion dominates

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The circuit dynamics constructed by traveling-wave parametric amplifiers (TWPA), using superconducting nonlinear asymmetric elements (SNAILs), are known to be approximately described by the Korteweg-de Vries (KdV) or modified KdV equations in the continuum limit and admit soliton solutions. The soliton spatially modulates the effective propagation velocity of the weak probe field, which leads to the effective realization of the causal structure of the analogue event horizons in the SNAIL-TWPA circuit system. In this paper, we derive the master equation for the weak probe field where the background soliton acts as an effective potential. We show the absence of normalizable negative modes in the SNAIL-TWPA circuit system by using the language of supersymmetric quantum mechanics. We also present the first study of quasi-normal modes (QNM) of the SNAIL-TWPA analogue black-white hole system by semi-analytic and numerical methods. Based on the resultant QNM frequency, we clarify the timescale at which nonlinear dispersion becomes effective in the SNAIL-TWPA circuit system and demonstrate how ringdown is excited.

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gr-qc 2026-05-13 2 theorems

Discrete relativistic body model yields six degrees of freedom

Dynamics of a relativistic discrete body: rigidity conditions, and covariant equations of motion

New rigidity conditions plus covariant equations permit more general motions than Born's theory.

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Rigidity conditions for a body considered as a discrete system of relativistic particles are proposed. They by themselves do not yet determine an evolution of the system, and some second-order equations must be added to them. Poincar\'e-covariant equations of motion compatible with these rigidity conditions are proposed and discussed. The resulting theory has the expected six dynamical degrees of freedom and therefore allows for more general motions than in Born's theory. Therefore, treating a relativistic body as a discrete system of particles could be a promising alternative to the standard approach based on Born's rigidity conditions.

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gr-qc 2026-05-13 2 theorems

Quantum corrections raise black hole ringdown frequencies

Bardeen spacetime as quantum corrected black hole: Grey-body factors and quasinormal modes of gravitational perturbations

Larger correction scales in the Bardeen metric increase the potential barrier, yielding higher frequencies and slower damping.

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We study axial gravitational perturbations of the asymptotically flat Bardeen spacetime interpreted as a string-T-duality-inspired quantum-corrected Schwarzschild black hole. Starting from the anisotropic-fluid background, we derive the Regge--Wheeler-type master equation and the corresponding effective potential, and compute quasinormal modes with high-order WKB--Pad\'e and time-domain methods. We show that increasing the quantum-correction scale $\ell_0$ raises and shifts the barrier inward, causing the black hole to ring at higher frequencies and decay more slowly. The same deformation suppresses low-frequency transmission, shifts the onset of grey-body factors to larger frequencies, and reorganizes the partial and total absorption cross-sections. Overall, the results identify a clear and consistent imprint of short-distance regularization on both ringdown and scattering observables.

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gr-qc 2026-05-12 2 theorems

Oscillating deceleration parameter models cyclic cosmic expansion

Periodic cosmic evolution in Hybrid and Logarithmic Teleparallel Gravity

Hybrid and logarithmic teleparallel gravity with q(t)=m cos(kt)-1 recovers present acceleration and alternates expansion phases.

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In this work, we investigate a cosmological model within modified teleparallel gravity using two functional forms of $f(T)$: a hybrid model $f(T)=e^{\gamma T}T^{\sigma}$ and a logarithmic model, in the context of a periodic cosmic evolution driven by an oscillating deceleration parameter $q(t)=m\cos(kt)-1$. This approach describes a cyclic Universe with successive transitions between decelerating and accelerating phases. By constraining the model with observational values $m \simeq 0.48$ and $H_0 = 69.2\,\text{km}\,\text{s}^{-1}\,\text{Mpc}^{-1}$, we recover the present accelerated expansion with $q_0 \approx -0.52$, while larger values $m \geq 1$ lead to strongly oscillatory regimes including super-acceleration. For the hybrid model ($\gamma = 0.1$, $\sigma = -0.5$), the energy density remains positive, while the pressure oscillates. The equation of state evolves dynamically, crossing both quintessence and phantom regimes. In contrast, the logarithmic model stabilizes the dynamics, regularizes divergences, and yields smoother evolution, with the equation of state mainly remaining in the quintessence regime. The analysis of energy conditions shows that the violation of the SEC supports accelerated expansion, while the partial validity of NEC and DEC ensures physical consistency. Overall, this framework provides a flexible alternative to the standard $\Lambda$CDM model, allowing a unified description of different phases of cosmic expansion.

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gr-qc 2026-05-12 Recognition

Closed dynamical system makes inflation an attractor to radiation

Closing the Cosmographic Hierarchy: Dynamical Attractors from Inflation to Reheating

Mapping slow-roll parameters into kinematic phase space closes the cosmographic hierarchy and shows radiation domination as the late-time re

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We develop a potential-independent cosmographic framework, in which cosmographic parameters are promoted to dynamical variables within a closed autonomous system. Although the cosmographic hierarchy is formally infinite, we achieve closure by mapping potential slow-roll parameters onto the kinematic phase space within General Relativity with a minimally coupled scalar field. Within this framework, we perform a stability analysis and show that inflationary (quasi-de Sitter) solutions arise as natural attractors, while stiff-fluid configurations act as repellers without invoking the slow-roll approximation. To describe the transition to standard Big Bang evolution, we extend the system to include a radiation component and a phenomenological decay term. This leads to a generalized, potential-independent description of reheating characterized by an effective equation of state $w_{\rm eff}$. We demonstrate that the radiation-dominated phase is the late-time attractor of the extended system. These results provide a unified kinematical description of the expansion history from inflation through reheating, bridging cosmography and scalar field dynamics.

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gr-qc 2026-05-12 Recognition

LLM agent builds analytic surrogate for eccentric black hole waves

Discovery of Interpretable Surrogates via Agentic AI: Application to Gravitational Waves

The model matches Advanced LIGO data to 6.9×10^{-4} mismatch and evaluates 8.4 times faster than full simulation.

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Fast surrogate models for expensive simulations are now essential across the sciences, yet they typically operate as black boxes. We present \texttt{GWAgent}, a large language model (LLM)-based workflow that constructs interpretable analytic surrogates directly from simulation data. Surrogate modeling is well suited to agentic workflows because candidate models can be quantitatively validated against ground-truth simulations at each iteration. As a demonstration, we build a surrogate for gravitational waveforms from eccentric binary black hole mergers. We show that providing the agent with a physics-informed domain ansatz substantially improves output model accuracy. The resulting analytic surrogate attains a median Advanced LIGO mismatch of $6.9\times10^{-4}$ together with an $\sim 8.4\times$ speedup in waveform evaluation, surpassing both symbolic regression and conventional machine learning baselines. Beyond producing an accurate model, the workflow identifies compact physical structure from the learned representation. As an astrophysical application, we use \texttt{GWAgent} to analyze the eccentricity of GW200129 and infer $e_{20\mathrm{Hz}}=0.099^{+0.063}_{-0.044}$. These results show that validation-constrained agentic workflows can produce accurate, fast, and interpretable surrogates for scientific simulations and inference.

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gr-qc 2026-05-12 Recognition

Transformer reads population properties straight from GW strain catalogs

End-to-End Population Inference from Gravitational-Wave Strain using Transformers

Dingo-Pop amortizes inference over 25-1000 events in one second and matches traditional posteriors without per-event sampling.

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The population of compact binaries encodes information about their astrophysical origins and the expansion of the universe. Hierarchical Bayesian methods infer these properties by combining single-event posteriors. As catalogs grow, however, this approach becomes computationally expensive and is subject to increasing Monte Carlo uncertainty. We introduce Dingo-Pop, a simulation-based framework that infers population posteriors directly from gravitational-wave strain data. The data for each event are embedded into low-dimensional tokens and combined using a transformer trained on simulated catalogs subject to selection effects. This enables (i) population inference without per-event Monte Carlo sampling noise, (ii) amortization across variable catalog sizes using a single network, and (iii) end-to-end inference in about one second. We train a network for catalog sizes of 25 to 1000 events, and obtain well-calibrated posteriors consistent with traditional methods. By avoiding per-event analyses that can take hours to days, Dingo-Pop enables new classes of large-scale injection studies; as an application, we examine how spectral-siren Hubble constant uncertainties change with catalog size.

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gr-qc 2026-05-12 2 theorems

LLM agents miss gravitational wave precision targets by 1-2 orders

gwBenchmarks: Stress-Testing LLM Agents on High-Precision Gravitational Wave Astronomy

Eight tasks from black hole orbital modeling and waveform construction reveal consistent accuracy shortfalls and invalid shortcuts.

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Modern gravitational wave astronomy relies on modeling tasks that often require months of graduate-level effort, including building fast waveform surrogates from expensive numerical relativity simulations, modeling orbital dynamics of black holes, fitting merger remnant properties and constructing template banks. These problems demand extreme precision to support detection and parameter inference, with state-of-the-art models achieving $\lesssim 10^{-4}$ relative error. We study whether state-of-the-art LLM coding agents can perform such end-to-end scientific modeling, where success requires constructing models with stringent accuracy criteria and reasoning about physical systems. We introduce gwBenchmarks, a suite of eight tasks grounded in gravitational wave analytic calculations and numerical simulations collectively representing over $10^8$ core-hours of compute. The tasks span interpolation, regression, and high-dimensional time-series modeling, requiring a combination of numerical methods, machine learning, and physics-informed approaches. In preliminary experiments, agents frequently relied on proxy metrics, partial evaluation, or fabricated results to spuriously complete tasks. We therefore implement an external pre-defined framework to gauge agent progress. Evaluating twelve coding agents, we find no consistent winner. On the easiest task, multiple agents converge to the same cubic spline solution, with one rediscovering a coordinate transformation widely used in the literature. On harder tasks like analytic waveform modeling, all agents fall 1-2 orders of magnitude short of domain requirements and exhibit systematic failures, including metric misuse, constraint violations, and result fabrication. Our code, data, and website are publicly available.

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gr-qc 2026-05-12 2 theorems

Traceful gauge reconstructs black-hole metrics from any source

Metric Reconstruction for Generic Black-Hole Perturbations

Two transport equations fix the trace from the stress-energy tensor; Newman-Penrose equations then complete the hierarchy in Petrov type D.

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Standard (radiation-gauge) metric reconstruction excludes generic sources because it requires a tracefree metric perturbation. We remove this obstruction for perturbations of Petrov type D spacetimes by introducing a traceful radiation gauge. Two first-order transport equations determine the metric trace from the stress-energy tensor, and the remaining metric components follow hierarchically from the Newman-Penrose equations. We illustrate the method for a Schwarzschild black hole with a thin static shell, including a source-supported static completion sector.

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gr-qc 2026-05-12 2 theorems

Cusps link initial black holes to final remnant in mergers

Cusp Formation in Merging Black Hole Horizons

Mass and higher multipoles at horizon cusps follow a phenomenological pattern that joins start and end states.

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An important question in binary black hole mergers is to connect properties of the remnant black hole to those of the two initial black holes. These properties include not only the final mass and spin of the remnant, but also higher multipoles and answers to other questions such as, for a given initial configuration, which quasi-normal modes of the final black hole are excited, and what are the amplitudes of these modes? Such questions have thus far been primarily addressed through a study of the emitted gravitational wave signal. In this paper we consider a different alternative, namely using quasi-local black hole horizons themselves to establish the link between the initial and final states. Recent work has elucidated the behavior of black hole horizons in a merger. Cusps forming in such otherwise smoothly evolving horizons have been shown to play a central role in connecting the two initially separate black holes with the final remnant. In the present work, we will discuss from a numerical perspective how such cusps form in detail for the head-on collision of two non-spinning black holes. We show how the mass and higher mass multipole moments behave at the cusp and suggest a phenomenological model.

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gr-qc 2026-05-12 2 theorems

Ultrasrelativistic collision produces secondary gravitational shockwave

Gravitational Waves in High Energy Fixed-Target Collisions

Linearized gravity yields an exact amplitude for the spherical wave and flux of radiation when a fast particle hits a massive target.

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The gravitational field of two-body system, a high energetic particle and a massive particle at rest, is studied in the linearized Einstein gravity. The ultrarelativistic particle yields a plane-fronted gravitational shockwave which perturbes gravitational field of the particle at rest. The problem can be also considered as a fixed-target high energy collision. We show that this collision is accompanied by the gravitational radiation, as is expected from the earlier results on the high-energy scattering. The new effect is a secondary spherical gravitational shockwave when the initial shockwave hits the massive particle. In the considered approximation the flux of gravitational radiation and the amplitude of the spherical shockwave are found in an analytic form. The suggested approach is also applicable when the null particle is replaced by plane null shells of a general profile. Implications of these effects for astrophysics are shortly discussed.

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gr-qc 2026-05-12 Recognition

Dirac field embeds consistently in LRS spacetimes

The Dirac field in LRS space-times: a covariant approach

Alignment of velocity and spin with congruence planes allows explicit solutions in types I, II and III.

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We employ the polar decomposition of the Dirac field to describe it as an effective spinorial fluid. We then construct a $(1+1+2)$ covariant formalism for the Dirac field that avoids the introduction of tetrad fields and Clifford matrices. Within this framework, we analyze the conditions under which a self-gravitating Dirac field can be consistently embedded in Locally Rotationally Symmetric (LRS) space-times of types I, II, and III. In accordance with the LRS symmetry requirements, we extend a previous work by assuming that the velocity and spin vector fields of the Dirac field lie in the planes defined pointwise by the generators of the time-like and space-like congruences, which underlie the $(1+1+2)$ decomposition. We present some analytical and numerical solutions to illustrate the applicability of the proposed framework.

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gr-qc 2026-05-12 Recognition

Minimal coupling adds branch EM sources to LV Raychaudhuri equation

Gauge-covariant Raychaudhuri dynamics for spin-nondegenerate Lorentz-violating congruences

The gauge-covariant momentum keeps dispersion branches fixed while electromagnetic fields contribute a divergence term to the expansion.

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We investigate the Raychaudhuri dynamics of charged spin--nondegenerate Lorentz--violating particle congruences under minimal electromagnetic coupling. The coupling is introduced through the gauge--covariant momentum $P_{\mu}=\pi_{\mu}-qA_{\mu}$, so that the branch dispersion relation keeps its free functional form, while the electromagnetic field enters through the evolution of $P_{\mu}$. For a generic branch $\mathcal D^{(\pm)}(P)$, the tangent $k^{\mu}_{(\pm)}$ and the momentum Hessian $M^{\mu\nu}_{(\pm)}$ determine the covariant acceleration, $a^{\mu}_{(\pm)}=-qM^{\mu\nu}_{(\pm)}F_{\nu\rho}k^{\rho}_{(\pm)}$. As a consequence, the Raychaudhuri equation acquires the branch-dependent electromagnetic source $-q\nabla_{\mu}\!\left(M^{\mu\nu}_{(\pm)}F_{\nu\rho}k^{\rho}_{(\pm)}\right)$. We apply this construction to the $b_{\mu}$, $H_{\mu\nu}$, and $d_{\mu\nu}$ sectors, obtaining the corresponding branch tangents, Hessians, accelerations, and focusing equations. In flat spacetime, the electromagnetic field modifies the expansion through the divergence of the effective branch force. Therefore, uniform fields may bend the trajectories, whereas local focusing requires field gradients or, in the magnetic case, a coupling to an already deformed congruence. We also develop the analogous description for semiclassical quasiparticle beams, where the band Hessian plays the role of an effective electromagnetic response tensor. For anisotropic parabolic, Dirac--like, and Weyl--type dispersions, the same geometric structure relates electromagnetic textures to beam focusing. In two-branch systems, the opposite Hessians of the branches can produce focusing in one congruence and defocusing in the other, giving a quasiparticle realization of branch--dependent birefringence.

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gr-qc 2026-05-12 2 theorems

Black hole spin and charge alter neutrino oscillation periods

Quantum Correlations of Neutrinos in the Kerr-Newman Space-time

Angular momentum lengthens periods of survival probability and entanglement for outward paths in the Kerr-Newman metric, while charge short

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Thanks to feeble interactions, neutrinos show special advantages in the field of quantum information (QM). The properties of quantum correlations (QCs) are fundamental for neutrino-based QM. In this paper, we investigate the influence of the Kerr--Newman metric on QCs by varying the metric parameters, namely the mass $M$, angular momentum per unit mass $a$, and charge $Q$. Both radial and non-radial neutrino propagation are considered under the weak-field approximation. The results show that, for inward propagation in the Kerr--Newman metric, the oscillation probabilities and QCs differ significantly from those obtained in the Schwarzschild metric. In the case of radial outward propagation, the angular momentum $a$ increases the oscillation period of the neutrino survival probability $P_{ee}$, entanglement, and nonlocality, whereas the charge $Q$ decreases the corresponding periods. For non-radial propagation, the modulation effects of $M$ and $a$ on the oscillation patterns of both probabilities and QCs become more pronounced. As $M$ increases, the oscillation probability remains within a higher-value range, whereas tripartite entanglement exhibits the opposite trend. Furthermore, our results reveal that, despite differences in their variation ranges, entanglement and coherence exhibit highly consistent oscillation behaviors in both radial and non-radial propagation cases. These findings provide broader quantitative support for the potential use of neutrinos as quantum information resources.

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gr-qc 2026-05-12 Recognition

UV-complete gravity restricts fifth forces to narrow wedge

Fifth-Force Constraints from UV-Complete Scalar-Tensor Gravity

The restriction excludes areas still permitted by experiments, so better searches can test these models.

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We study an $O(N)$ scalar multiplet nonminimally coupled to gravity and follow its renormalization-group (RG) flow in the vicinity of an interacting, nonperturbatively UV-complete scaling regime of scalar-tensor theory. In the broken phase, the radial mode mediates a universal Yukawa correction to Newtonian gravity, parametrized by a strength $\alpha$ and range $\lambda$. Imposing UV completeness -- regular RG trajectories that reach the UV scaling regime -- restricts the infrared data to a finite wedge, which maps to a narrow region in the $(\alpha,\lambda)$ plane. Its complement is, therefore, ruled out by UV completeness alone. Remarkably, part of this theory-excluded domain lies below current experimental exclusion envelopes, so improved fifth-force searches can directly test and potentially falsify this class of UV-complete scalar-tensor models.

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gr-qc 2026-05-12 2 theorems

BB plot validates Bayes factor accuracy via distribution relationship

BB plot: A Tool for Accurate Model Selection Using Bayes factors

The diagnostic links computed factors to their expected densities under competing models, enabling cheap background estimates for GW events.

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A common task in physics and astronomy is studying which of the competing hypotheses the data prefer. This is usually done by computing the Bayes factor between the two hypotheses, and either interpreting it in terms of the posterior odds or as a ranking statistic for a frequentist p-value test. Here we describe a relationship between the Bayes factor and its distributions under the two competing hypotheses, called the Bayes factor-Bayes factor (BB) relationship, expressed as a diagnostic plot. Using examples from gravitational wave (GW) astronomy, we demonstrate how the BB plot can validate the accuracy of Bayes factor calculations. The BB relationship may also be useful for estimating background distributions of the Bayes factor at low computational cost, even analytically in some cases. We apply this technique in the context of wave-optics lensing of GWs, extrapolating the background distribution from GWTC4 to put a rough bound of $\lesssim 4.1 \sigma$ on the statistical significance of GW231123.

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gr-qc 2026-05-12 Recognition

Expansion factor alters Jeans criterion to seed galaxies from short waves

A study on Dusty Plasma Physics and the examination of Jeans Criteria for the Milky Way

In the Einstein-de Sitter model the time-dependent critical wavenumber permits short-wavelength modes during inflation to drive collapse and

abstract click to expand

Since the early 1990s, there has been significant interest in the physics of dusty plasmas, which has now become a new discipline in plasma science. Dusty plasma exhibits new and unusual behaviour, and provides a possibility for modified or entirely new collective modes of oscillations, instabilities as well as coherent nonlinear structures.\\ First, a review of the important recurring terms -- The Cosmic Waves (CRs), the Alfven Waves (AWs), and the associated charged dust grains is presented. Starting from the basic composition of the CRs to their scattering mechanism, along with the different modes of scattering, is presented, along with the modes of confinement and a precise definition of each term. The paper also includes some useful diagrams and brief notes from the references. \\ Gravitation plays a significant role in the collapse of matter and the formation of cosmological structures. Unlike a static universe, this paper investigates the Jeans instability in a radiation-pressure-dominated expanding universe using the Einstein-de Sitter model for Euclidean geometry with zero curvature ($\kappa=0$). The fluid model for an expanding universe is constructed, and by taking small perturbations, the perturbed fluid equations are obtained. The dispersion relation of gravitational instability is derived using plane-wave solutions. In the static case (Newtonian cosmology), the classical Jeans instability criterion is revisited and modified in an expanding universe. The critical Jeans wave number of perturbations to excite Jeans instability depends upon the time-dependent expansion factor $S(t)$. It is found that short-wavelength perturbations are expected during the inflationary period of big bang cosmology, which are responsible for gravitational collapse and the formation of galaxies.

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gr-qc 2026-05-12 2 theorems

Two families of regular hairy black holes from gravitational decoupling

Regular hairy black holes by gravitational decoupling: Bardeen and Minkowski-core seeds

One family produces a de Sitter-like core while the other has vanishing central density, with horizon structures determined for varying变形

abstract click to expand

We construct two families of regular hairy black holes within gravitational decoupling using a fixed exponential deformation profile for an effective tensor-vacuum sector. The first family is generated from a Bardeen-type seed and produces a de Sitter-like core. The second family is generated from a hollow seed with an asymptotically Minkowski core so that the central density vanishes and no de Sitter core is produced. For each branch we determine the critical deformation strengths separating horizonless, extremal, and two-horizon geometries in the static case, and we obtain the corresponding Kerr-like rotating extension by promoting the mass parameter to the deformed mass function. Representative parameter choices are used to illustrate the horizon structure and to verify the weak energy condition in the exterior region.

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gr-qc 2026-05-12 1 theorem

Quantum gravity adds irreducible noise to parallel atom beams

Quantum gravitational deflection of parallel matter wave beams

Two parallel matter-wave beams acquire a tidal spread in separation that classical gravity cannot remove.

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It is well known that two parallel photon beams do not deflect under the effect of their energy-momentum tensor. In this work, we propose a novel model where two spatially separated Bose-Einstein condensates are outcoupled to create two parallel atom laser beams. We find out that apart from the classical deflection, a purely quantum gravity induced tidal deflection is observed which results in an irreducible noise in the geodesic separation of the two beams. Based on this simple but novel theoretical outcome, we propose an experimental model for detecting this quantum gravity induced standard deviation in the geodesic separation of the two parallel matter-wave beams.

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gr-qc 2026-05-11 2 theorems

Misner strings carry gravielectric fluxes between horizon and infinity

Gravielectric and gravimagnetic fluxes in nutty black holes

Lateral transparency lets field lines cross the strings, turning negative Komar integrals into evidence of closed circuits rather than unphy

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We introduce the gravielectric (GE) and gravimagnetic (GM) fields in stationary spacetime using the Komar two-form and its dual. This opens the way to extend the Komar-Tomimatsu derivation of mass formulas to a more detailed picture in terms of the local lines of force. We show that Misner strings (MS) carry singular GE and GM fluxes connecting the horizon and the asymptotic zone. Moreover, MS are laterally transparent, so field lines can flow in and out of the bulk. This explains why the usual Komar mass integrals around the Misner strings in the Taub-NUT vacuum solution are negative: the pattern of field lines shows that they flow onto the string from the horizon, so it is necessary to calculate the incoming (positive) but not the outgoing Komar fluxes. This incoming flux is then turned back to the horizon through the Misner strings, realizing the closed circuit without sources. So Misner strings are massless empty tubes, but not rigid rods of negative mass. Similarly, GM field lines can connect positively and negatively charged regions of the horizon, generating, for example, the gravimagnetic dipole moment of the Kerr metric.

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gr-qc 2026-05-11 2 theorems

External demon extracts less work near black hole horizon

Quantum Maxwell Demon at the Black Hole Horizon: Thermodynamics, Information, and the Equivalence Principle

Information loss at the horizon reduces performance for outside observers, but local thermodynamics holds both inside and out.

abstract click to expand

We analyze a quantum Maxwell demon operating a Szilard engine in free fall near a black hole horizon, where quantum information, thermodynamics, and spacetime causality intersect. The demon is modeled as a coherent two-level system, and the working substance is a single particle in a one-dimensional chamber crossing the event horizon. As the chamber crosses the horizon, the particle's Hilbert space splits into accessible and inaccessible sectors, leading to non-unitary reduced dynamics for an external demon due to tracing over interior degrees of freedom. We construct explicit measurement, expansion, and wall removal protocols for demons located outside or inside the horizon. Our results show that an external demon experiences degraded measurement correlations and reduced work extraction due to horizon-induced information loss, yet still obeys local thermodynamics and Landauer's principle. For an internal demon, the protocol reduces locally to the flat spacetime case, preserving the equivalence principle at the level of dynamics. While the equivalence principle holds dynamically, quantum information processing provides an operational signature of the horizon through reduced accessibility and irreversible open system behavior, clarifying how information, causality, and thermodynamics coexist in black-hole spacetimes.

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gr-qc 2026-05-11 2 theorems

Pure Lovelock black holes radiate far less than Einstein ones

Hawking Radiation and Greybody Factors of Test Scalar and Electromagnetic Fields on Asymptotically Flat Pure Lovelock Black Holes

Lower temperature cuts scalar power by 10^{-3} and electromagnetic power by 10^{-5} in six dimensions despite higher transparency.

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Pure Lovelock black holes are geometrically more transparent than their Einstein counterparts, but they radiate far less. We compute scalar and higher-dimensional electromagnetic greybody factors and Hawking spectra on the critical branch $d=2N+2$, compare them with Schwarzschild--Tangherlini black holes at the same horizon radius $r_h$, and show that the smaller Hawking temperature overwhelms the enhanced transmission. In the benchmark $d=6$ case, the integrated scalar and electromagnetic powers are reduced by about $10^{-3}$ and $10^{-5}$, respectively. We also find a clean higher-curvature signature: as the Lovelock order $N$ grows, Hawking radiation becomes increasingly dominated by the scalar-type electromagnetic sector.

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gr-qc 2026-05-11 2 theorems

GW and EM distances test Friedmann model without dark energy

Multimessenger consistency tests of the Friedmann cosmological model

A curvature relation derived from paired luminosity distances yields consistency conditions that hold for any dark energy model.

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We show that within the framework of the Friedmann cosmological model it is possible to derive general multimessenger consistency conditions, independent of the form of dark energy. We first derive a general relation for the curvature parameter, uniquely in terms of the gravitational wave (GW) and the electromagnetic wave (EMW) luminosity distances, which can be used to probe the curvature of the Universe with multimessenger astronomy, independently of the dark energy equation of state. We then use this to derive a general multimessenger consistency relation for the Friedmann model, independent of the dark energy model and of cosmological density parameters. As a special case, a multimessenger consistency test for the cosmological constant is also derived, independent of the curvature and matter density parameters.

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gr-qc 2026-05-11 2 theorems

Scalar mass sharply reduces black hole mode damping

Massive Scalar Quasinormal Modes, Greybody Factors, and Absorption Cross Section of a Parity-Symmetric Beyond-Horndeski Black Hole

Higher masses drive quasinormal modes toward long-lived states while massive tails dominate the signal earlier in parity-symmetric beyond-Ho

abstract click to expand

We study quasinormal modes, greybody factors, and the absorption cross section of a massive scalar field in the asymptotically flat parity-symmetric beyond-Horndeski black-hole background. The scalar mass raises the asymptotic level of the effective potential and can eliminate its barrier peak, thereby changing both the ringing spectrum and the scattering characteristics relative to the massless case. Using Pad\'e-improved high-order WKB calculations together with time-domain evolution, we find that the damping rate decreases strongly as the field mass increases, indicating the approach to long-lived quasi-resonant states for representative parameter families. At the same time, in the large-mass regime these weakly damped modes become progressively harder to isolate in the time domain, because the oscillatory massive tails are expected to dominate on the Koyama--Tomimatsu scale $\mu_s t\gg \mu_s M$, which is comparatively early when $M=1$ and $\mu_s$ is not small. The time-domain profiles also exhibit the transition from quasinormal ringing to an oscillatory late-time tail. Interpreting the same effective potential semiclassically, we show that increasing the scalar mass suppresses low-frequency transmission and shifts the onset of efficient absorption to higher frequencies, while larger deviations from the Schwarzschild limit enhance the absorption cross section. These results show that the competition between long-lived modes and rapidly dominant massive tails makes the massive sector an especially subtle and sensitive probe of the interplay between field mass and geometric deformation in this class of black holes.

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gr-qc 2026-05-11 2 theorems

Rotation boosts resonant peaks in wormhole scalar waves

Resonant transmission of scalar waves through rotating traversable wormhole

Numerical spectra for Teo wormholes show stronger Breit-Wigner resonances when rotation is included, marking a potential observable contrast

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The viability of traversable wormholes as exotic compact objects requires the identification of signatures that distinguish them from other compact objects. Given recent advances in observing rotating black hole signatures, identifying characteristic imprints that reflect the absence of an event horizon and the presence of a throat structure is of considerable significance. Motivated by this, in the present work, we analyze the propagation of a massless scalar field in a rotating traversable wormhole spacetime described by Teo's class of solutions. We numerically compute the transmission (greybody) factor and the corresponding absorption spectrum across a broad range of frequencies. The spectrum exhibits a series of sharp peaks in the amplitudes, which we identify as Breit-Wigner-type resonances. The emergence of such peaks can be attributed to the scalar modes temporarily trapped within the potential well formed by barriers on either side of the throat. These resonant features, previously identified in static wormhole backgrounds, persist in the rotating case. In particular, for Teo's class of wormholes, we find that rotation enhances the strength of the resonances. Overall, our results demonstrate the role of rotation in shaping the resonance effect and indicate these features as characteristic signatures of wormhole geometries.

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gr-qc 2026-05-11 Recognition

Heun functions cut flux computation time for generic Kerr orbits by up to 60x

Efficient and Stable Computation of Gravitational-Wave Fluxes from Generic Kerr Orbits via a Unified HeunC Framework

New framework reaches 10^{-11} accuracy for summed radiative fluxes while reducing costs versus standard packages.

abstract click to expand

Modeling extreme-mass-ratio inspirals hinges on the accurate and efficient computation of gravitational-wave fluxes from generic Kerr orbits. Conventional frequency-domain techniques are often limited by costly auxiliary parameter searches and numerical instabilities in the strong-field or high-frequency regimes. We address these challenges by reformulating both the angular and radial Teukolsky equations in terms of confluent Heun functions. Employing a hybrid analytic continuation algorithm to compute the connection coefficients eliminates the dependence on auxiliary parameters, directly yielding globally convergent solutions and scattering amplitudes. To resolve the highly oscillatory source integrands for generic orbits, we implement an adaptive bi-power mapping quadrature. Comprehensive benchmarks under standard double-precision arithmetic demonstrate that, for the total radiative flux summed over 168 low-order modes, our method achieves relative errors of order $10^{-11}$, with computational costs typically reduced by factors of 3--13 compared to the state-of-the-art GeneralizedSasakiNakamura. jl and pybhpt packages. Notably, for highly oscillatory high-order modes, our framework achieves a speedup of up to 60 times compared to specialized oscillatory integrators like GeneralizedSasakiNakamura. jl. These demonstrated gains in precision and efficiency establish the framework as a robust tool for strong-field perturbation theory, providing the numerical foundation for high-order self-force calculations and rapid, high-precision waveform generation.

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gr-qc 2026-05-11 Recognition

HeunC method computes Kerr orbit fluxes at 10^{-11} precision faster

Efficient and Stable Computation of Gravitational-Wave Fluxes from Generic Kerr Orbits via a Unified HeunC Framework

Reformulation eliminates auxiliary parameter searches and stabilizes strong-field generic-orbit calculations for extreme-mass-ratio inspirar

abstract click to expand

Modeling extreme-mass-ratio inspirals hinges on the accurate and efficient computation of gravitational-wave fluxes from generic Kerr orbits. Conventional frequency-domain techniques are often limited by costly auxiliary parameter searches and numerical instabilities in the strong-field or high-frequency regimes. We address these challenges by reformulating both the angular and radial Teukolsky equations in terms of confluent Heun functions. Employing a hybrid analytic continuation algorithm to compute the connection coefficients eliminates the dependence on auxiliary parameters, directly yielding globally convergent solutions and scattering amplitudes. To resolve the highly oscillatory source integrands for generic orbits, we implement an adaptive bi-power mapping quadrature. Comprehensive benchmarks under standard double-precision arithmetic demonstrate that, for the total radiative flux summed over 168 low-order modes, our method achieves relative errors of order $10^{-11}$, with computational costs typically reduced by factors of 3--13 compared to the state-of-the-art GeneralizedSasakiNakamura. jl and pybhpt packages. Notably, for highly oscillatory high-order modes, our framework achieves a speedup of up to 60 times compared to specialized oscillatory integrators like GeneralizedSasakiNakamura. jl. These demonstrated gains in precision and efficiency establish the framework as a robust tool for strong-field perturbation theory, providing the numerical foundation for high-order self-force calculations and rapid, high-precision waveform generation.

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gr-qc 2026-05-11 Recognition

Effective tensor reformulation keeps f(R,T) gravity EoS-independent

Neutron stars in a conservative f(R,T) gravity

Allows neutron-star mass-radius and tidal predictions with realistic equations of state while satisfying conservation from field equations.

abstract click to expand

We investigate a conservative formulation of $f(R,T)$ gravity motivated by a key limitation of several existing approaches: the gravitational function is often reconstructed from a chosen equation of state, making the gravity sector EoS-dependent and compromising universality. To avoid this problem, we reformulate the theory in terms of an effective energy-momentum tensor, so that the conservation law follows from the field equations and Bianchi identities while the gravitational action remains independent of the microphysical EoS. We derive the modified stellar structure equations, establish theoretical consistency conditions including coupling bounds and crust-singularity avoidance, and present the tidal perturbation sector in terms of effective thermodynamic variables and an effective sound speed. We then compute neutron star observables using realistic tabulated EoSs, including mass-radius relations and tidal deformabilities, and compare the model with current astrophysical constraints from massive pulsars, NICER radius measurements, and GW170817.

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gr-qc 2026-05-11 Recognition

Higher-curvature terms shift photon spheres in black holes

Photon Sphere and Shadow of a Perturbative Black Hole in f(R,mathcal{G}) Gravity

Perturbative f(R,G) gravity modifies unstable photon orbits and the resulting shadow size at leading order.

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We investigate the impact of higher-curvature corrections on black-hole observables within a perturbative $f(R, G)$ gravity framework. Working in a static, spherically symmetric spacetime, we construct leading-order deviations from the Schwarzschild solution by expanding the field equations in small coupling parameters associated with quadratic curvature invariants. The resulting metric corrections are obtained as asymptotic expansions and used to analyze null geodesics. We derive analytic expressions for the shift in the photon-sphere radius and show that higher-curvature terms modify the location of unstable photon orbits, with the Gauss--Bonnet sector producing a more significant contribution than mixed curvature terms. These modifications propagate to observable quantities, leading to corrections in the black-hole shadow radius. We identify the distinct roles of photon-sphere displacement and direct metric perturbations in determining the shadow size. We further discuss the implications of these corrections for strong gravitational lensing and quasinormal modes, highlighting the enhanced sensitivity of strong-field observables to higher-curvature effects. While the present analysis is based on an asymptotic perturbative treatment, our results provide a consistent framework for estimating leading-order deviations from general relativity and suggest that high-resolution observations, including very-long-baseline interferometry and gravitational-wave measurements, may offer constraints on modified gravity models.

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gr-qc 2026-05-11 3 theorems

f(R,G) gravity fits CC and Pantheon+ data for late acceleration

Late-Time Cosmic Acceleration in Ricci-Gauss-Bonnet Gravity via Gradient Descent Optimization

Parametrized Ricci-Gauss-Bonnet model shows quintessence behavior, satisfies energy conditions, and matches universe age estimates.

abstract click to expand

We study the late-time evolution of the Universe within the f(R,G) gravity framework, where R is the Ricci scalar and G is the Gauss-Bonnet term. To make the model tractable, we propose a parametrization scheme and determine its parameters using Gradient Descent, with constraints coming from the latest Cosmic Chronometer (CC) and Pantheon+ supernova data. Key cosmological indicators, namely the deceleration parameter q and the equation-of-state parameter w, show a clear transition from past deceleration to the present accelerated expansion. Interestingly, the equation-of-state parameter w remains above the phantom divide, indicating quintessence-like behavior consistent with current observations. Energy-condition analysis further supports this framework: the strong energy condition is violated, consistent with models allowing cosmic acceleration, whereas both the weak and null energy conditions remain satisfied. To test consistency, we also apply the Om(z) diagnostic, which distinguishes this model from the standard cosmological constant scenario and indicates a quintessence-dominated future evolution. Using the best-fit values, we estimate the age of the Universe, obtaining good agreement with independent astrophysical measurements. Overall, the results suggest that f(R,G) gravity provides a viable and self-consistent explanation for late-time cosmic acceleration when constrained using the combined CC and Pantheon+ datasets.

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gr-qc 2026-05-11 2 theorems

Algebraic map converts star density into exterior geometry

Matter Maps to Geometry in Gravitational Collapse

Generalized Oppenheimer-Snyder collapse turns differential Einstein equations into a direct bidirectional correspondence.

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We establish an exact bidirectional map between interior Friedmann density of a collapsing star and exterior static spherically symmetric metric in generalized Oppenheimer-Snyder collapse. This reduces Einstein's differential matter-geometry relation to an algebraic form, generating classical or quantum-corrected metrics and dynamics without solving field equations. Correction powers diagnose models: integer exponents signal ultraviolet completions, while fractional powers identify phenomenological ones. Our framework enables systematic tests of singularity resolution and cosmic censorship.

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gr-qc 2026-05-11 2 theorems

Radial black-hole infall waveform reaches 3.5PN order

Gravitational waveform from radial infall at the third-and-half Post-Newtonian order

The analytic result includes radiation-reaction effects in both the motion and the emitted waves before the final capture.

abstract click to expand

We compute the gravitational waveform associated with a radially infalling particle in a Schwarzschild black hole working in the center-of-mass system and in a post-Newtonian (PN) approximation. Our results reach the highest accuracy level fully displayed in the literature, namely the 3.5PN order. The latter accuracy includes both conservative and radiation-reaction contributions (at 2.5PN and 3.5PN) in the two-body dynamics, and corresponding effects in the waveform too. The apparent simplicity of the radial fall (namely, the 1-dimensional motion) contrasts with the peculiarity of the process which will end necessarily with the capture of the particle by the black hole, featuring strong field effects. In other words, our analysis being limited to the region of validity of the PN approximation, cannot capture (by definition of PN approximation) the final phase of the fall, but offers significant insights anyway.

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gr-qc 2026-05-11 3 theorems

f(R,T) gravity model fits data and approaches de Sitter phase

Anisotropic Cosmology with interacting Dark Energy in f(R,T) Gravity: A Data-Constrained & independent Approach

Reconstructed anisotropic expansion history matches observations and shows quintessence-like behavior at late times.

abstract click to expand

In this work, we investigate the cosmological dynamics of an anisotropic Universe within the framework of $f(R,T)$ gravity by incorporating pressureless dark matter and the dark energy models. The analysis is carried out in a Bianchi type-I space-time, allowing us to capture possible deviations from isotropy and their evolution during cosmic expansion. A phenomenological reconstruction scheme based on a variable deceleration parameter is adopted to derive a redshift-dependent Hubble function. To establish observational viability, we constrain the free parameters of the model using a comprehensive statistical analysis that combines observational Hubble data and the Pantheon+ Type Ia supernova compilation. The resulting parameter space is tightly bounded, and the reconstructed expansion history exhibits strong consistency with current observational expectations. The model successfully reproduces the transition from an early decelerating phase to the present accelerated epoch, while asymptotically approaching a de Sitter-like regime. Further we analyzed the geometrical diagnostics, including the statefinder and $O_m$ diagnostics, which indicate a close correspondence with the standard $\Lambda$CDM scenario at late times. The behavior of the effective equation of state suggests a dynamically evolving dark energy component consistent with a quintessence-like regime. Additionally, the analysis of energy conditions confirms the physical admissibility of the model, whereas the stability investigation reveals the presence of classical instabilities at the perturbative level.

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gr-qc 2026-05-11 2 theorems

Differential forms unify Grad-Shafranov equation

General Grad-Shafranov Equation

One general expression recovers all special cases for symmetric force-free fields and equals the on-shell condition of a scalar Lagrangian.

abstract click to expand

To effectively describe the plasma with strong magnetic field, the force-free electrodynamics was introduced, within which the Grad-Shafranov equation plays the key role. The Grad-Shafranov equation governs the global structure of a electromagnetic field in equilibrium with symmetries. It is widely applicable in an amount of scenarios, such as the tokamak, the solar corona, the magnetosphere of Earth, neutron star and black hole, etc. However, in different situations, the Grad-Shafranov equation is expressed differently, and the derivations might be complicated. In this work, via the language of differential form, we provide a general expression of Grad-Shafranov equation, from which the expression in any specific situation can be quickly obtained. Additionally, we present a Lagrangian density for a scalar field whose on-shell condition is precisely the Grad-Shafranov equation.

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gr-qc 2026-05-11 2 theorems

Formulas extract black hole mass from orbital frequency shifts

Black hole mass and distance from accretion disk astrophysical observables

Symmetric observations and redshift rapidity give independent expressions for mass, distance and orbital radius in Schwarzschild spacetimes.

abstract click to expand

In this work we derive novel analytical expressions for the mass and distance of a Schwarzschild black hole (BH), as well as for the orbital radius of test particles orbiting it, it terms of astrophysical observables measured throughout the entire orbit of the revolving particle. We use a general relativistic method to describe the frequency shifts of photons emitted in the vivinity of a BH by considering two emitters (or two positions of the same emitter) located symmetrically opposite to each other with respect to the observer's line of sight (LOS) when performing measurements along the orbit. Furthermore, the introduction of the redshift rapidity allows us to write independent expressions for the BH mass and its distance to Earth. We also extend our study to the case when astrophysical systems have a peculiar motion and derive the corresponding closed formulas.

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gr-qc 2026-05-11 Recognition

Relativistic f-mode sums match neutron-star tides to 3 percent

The Good, the Bad, and the Subtle: Relativistic mode sums for neutron-star tidal response

Practical mode-sum calculation reproduces direct results for the dominant mode despite non-positive inner products and field ambiguities

abstract click to expand

Time-dependent tidal interactions during the late inspiral of binary neutron stars encode valuable information about neutron-star structure, but systematically extending the familiar Newtonian mode-sum picture into full general relativity is nontrivial. In this paper, we develop a practical relativistic implementation of mode-sum tidal response for non-rotating neutron stars in Regge-Wheeler gauge. Using near-zone boundary conditions, we systematically define the interior tidal field, the relativistic overlap integrals, and the corresponding mode amplitudes. The good is that the dominant f-mode contribution is remarkably robust, reproducing the direct matching calculation to within $\sim 3$\% across the equations of state we consider. The bad is that the operator governing mode inner product is not positive definite on the full Regge-Wheeler-gauge function space, so the relativistic mode sum truncated at ${\cal{O}}(\omega^2)$ is not expected to strictly converge to the direct matching solution. The subtle is that the tidal field inside the star is not unique, although this ambiguity has only a limited impact on the dominant f-mode response for the classes of extensions studied here. Our results establish the practical utility of relativistic mode-sum approximations, while making clear that their predictive power comes from a controlled low-mode description, rather than from a formally convergent strong-field expansion.

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gr-qc 2026-05-11 2 theorems

Negative-mass binaries would emit anti-chirps and runaways unseen in data

Unique Gravitational-Wave Signals from Negative-Mass Binaries

Their dynamics produce signals absent from current observations, ruling out negative masses without modified gravity assumptions.

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Negative masses have long been explored, but their observational viability remains unclear. In this work, we develop a unified, observationally testable framework to constrain negative masses using both coupling level and dynamical probes. We establish that while dipole radiation bounds require universality of gravitational charge, the intrinsic dynamics of negative mass binaries generically lead to anomalous behaviors such as anti-chirps, dispersal and runaway motion. These signatures are absent in current gravitational wave observations, providing a robust exclusion channel independent of modified gravity assumptions.

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gr-qc 2026-05-11 3 theorems

Coherent states show no temporal Bell violation in inflation

Bipartite temporal Bell inequality for squeezed coherent state of inflationary perturbations

Exact results for coherent and squeezed coherent initial conditions stay below the bound, so state distinction relies on other signatures.

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We investigate the role of the bipartite temporal Bell inequality, an analogue of the spatial Bell inequality, in probing the quantum imprints of primordial perturbations when the initially chosen Bunch-Davies vacuum is replaced by a coherent state. Although it is based on the same principles of locality and realism, its primary advantage lies in the fact that it does not require two distinct set of observable for its construction. Instead, measurements performed on a single component of the pseudo-spin operator at different times are sufficient. Consequently, it is particularly well suited for cosmological scenarios, where observational constraints typically allow access to only one component of the pseudo-spin operator. Assuming a coherent state as the initial condition, we derive an analytical expression for the expectation value of the bipartite temporal Bell operator and demonstrate the absence of temporal Bell violation in such a scenario. Interestingly, the results for squeezed coherent state is found to differ - albeit slightly - from those of squeezed vacuum state for large values of the squeezing parameter. This suggests that the ability to distinguish among different initial states of primordial perturbations does not rely on the violation of temporal Bell inequality. Furthermore, the dependence of the temporal Bell inequality on a purely imaginary phase factor of the wave function appears to be an unique feature, which is entirely absent in the context of spatial Bell inequalities.

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gr-qc 2026-05-11 2 theorems

Uncertainty principles change the maximum entropic force

Uncertainty Principles and Maximum Entropic Force

The corrected force depends on the specific quantum gravity parameters and, for extended cases, on the number of Planck areas involved.

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We consider quantum gravity corrections to the maximum entropic force that arise from several gravitational uncertainty principles. These include the Generalized Uncertainty Principle (GUP), the Extended Uncertainty Principle (EUP), the Generalized Extended Uncertainty Principle (GEUP), and the Linear-Quadratic GUP (LQGUP). We find that the modified entropic force depends on the dimensionless parameters of the uncertainty principles and, thus, on the underlying quantum gravity theory. Furthermore, the entropic force, which is quantum gravity corrected in the framework of the extended uncertainty principles, also depends on the number of Planck areas that made the ``EUP area".

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gr-qc 2026-05-11 Recognition

Percent-level memory deviations found in beyond-GR gravity

Gravitational Wave Memory in Beyond GR Theories

First full inspiral-merger-ringdown computation in scalar Gauss-Bonnet theory shows merger-driven changes and suppressed scalar effects.

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Gravitational-wave memory is a low-frequency, non-oscillatory signal that provides a promising probe of strong-field gravity. We present the first computation of memory from full inspiral--merger--ringdown waveforms in a theory beyond GR, focusing on scalar Gauss--Bonnet gravity. We find percent-level deviations from GR, mainly driven by modified merger dynamics, while scalar-induced contributions to tensor memory are strongly suppressed. We found that including memory greatly enhances the mismatch between GR and beyond-GR waveforms, highlighting its potential as a complementary observable for tests of gravity with next-generation detectors.

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gr-qc 2026-05-11 2 theorems

Quantum gravity turns black hole formation into fuzzy-nova ejection

Fuzzy-novae

Simulations show local quantum repulsion creates an outgoing matter wave that ejects all mass from collapsing stars, avoiding singularities.

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We propose a novel phenomenological model of quantum gravitational collapse inspired by loop quantum gravity that ensures a completely regular spacetime evolution. By incorporating quantum gravitational modifications based on local rather than average energy density, our model simultaneously resolves both the central singularity and the shell-crossing singularities. Numerical simulations reveal that the interplay between local quantum repulsion and gravitational attraction leads to the formation of a stable, outgoing solitary matter wave, supported by a dynamical local anti-trapped region. This mechanism allows for a time-like ejection of the entire stellar mass -- a \emph{fuzzy-nova} -- which signals the end of macroscopic black holes. By providing a concrete dynamical mechanism for matter to escape the trapped region, our work sets a new stage for resolving the information paradox and opens a realistic observational window into quantum gravity.

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gr-qc 2026-05-11 2 theorems

Scalar charge jump at merger adds new memory signal in modified gravity

Scalar memory from compact binary coalescences

For events like GW150914 the extra breathing polarization changes the low-frequency offset by an amount comparable to existing corrections.

abstract click to expand

Gravitational memory provides a distinctive low-frequency probe of gravity, but explicit merger studies beyond general relativity remain limited. In this work, we investigate memory from binary black hole mergers in Ricci-coupled scalar-Gauss-Bonnet gravity, a natural extension of scalar-Gauss-Bonnet theory that admits an additional scalar breathing polarization. Based on numerical-relativity waveforms of binary black hole coalescences, we show that the change in the scalar charge of the system across merger generates a significant scalar-memory contribution. For a GW150914-like system, this effect modifies the memory signal in a gravitational-wave detector on the same observable timescale and by an amount comparable to the pure scalar-Gauss-Bonnet correction to tensor memory. Thus, it can substantially enhance the total deviation from the general-relativity prediction over a broad range of source and detector configurations. We argue that this identifies a general mechanism: whenever a compact-binary merger changes the asymptotic charge of an additional gravitational field, and that field sources an observable extra polarization, the resulting memory can provide a leading low-frequency signature of new gravitational physics.

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gr-qc 2026-05-11 2 theorems

Quadratic pre-geometric gravity sets dark energy scale via gravi-axion

DESI and Dynamical Dark Energy from Extended Pre-geometric Gravity

The model matches DESI BAO+FS data with reduced chi-squared 1.394 and only percent-level deviation in slip parameter from Lambda CDM.

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We consider the simplest quadratic extension of MacDowell-Mansouri pre-geometric gravity preserving the topological pre-volume form symmetry. After symmetry breaking, it becomes $(\mathrm{Lovelock})^2$ gravity, dual to a Galileon-like Horndeski scalar-tensor theory. The gravitational Higgs mechanism forces the Gauss-Bonnet coupling to be inversely proportional to the bare cosmological constant. The quadratic correction renders the gravitational $\theta$-angle dynamical in the form of a gravi-axion, whose effective mass sets the dark energy scale, thus naturally realizing a dynamical dark energy. The model fits DESI's BAO+FS data exceptionally well ($\chi^2_{\rm red} = 1.394$), deviating from $\Lambda\mathrm{CDM}$ by only a few percent in the gravitational slip parameter $\gamma(z)$ with stable tensor perturbations. This analysis establishes a concrete, testable bridge between pre-geometric gravity and cosmic acceleration.

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gr-qc 2026-05-11 Recognition

Black holes need extra pressure term for thermodynamics at finite distance

Black holes at a finite distance: Quasi-local restricted phase space formalism

Adding the area and pressure of the surface where observers sit lets the first law hold and reveals new phase transitions absent at infinity

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We extend the restricted phase space formalism for spherically symmetric black hole solutions of Einstein-Maxwell theory to the quasi-local regime, with the static observers located at a finite radial distance. The first law and Euler relation for the RN and RN-AdS black holes are proved to hold, but only with the inclusion of an extra pair of thermodynamic variables, i.e. the pressure and the area of the codimension-2 hypersurface on which the observers reside. For the RN black holes, the quasi-local behavior is analyzed in detail. It turns out that the RN black holes in the quasi-local description behaves significantly different from itself in the asymptotic description, but is extremely similar to the RN-AdS black holes in the asymptotic description, e.g. allowing for isocharge temperature-entropy phase transitions and lack of isovoltage temperature-entropy phase transitions. In the neutral limit, the Hawking-Page-like transitions appear in the quasi-local description which is absent in the asymptotic description.

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gr-qc 2026-05-11 2 theorems

f(Q) gravity sustains stable traversable wormholes

Traversable wormholes in boldsymbol{f(Q)} gravity: Energy conditions, stability and quasinormal modes

Power-law models give analytic solutions with energy violations confined to the throat and perturbations that damp over time.

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We investigate static and spherically symmetric traversable wormhole solutions in the framework of $f(Q)$ gravity by considering a power-law model of the form $f(Q)=\gamma(-Q)^m$. By adopting an anisotropic matter distribution and imposing an equation of state relating the radial pressure and energy density, we obtain an analytic shape function that satisfies the geometric requirements for a traversable wormhole. The model parameter is constrained to $0<m<1/2$, corresponding to a quintessence-like regime with $-1<\omega<-1/3$. The energy conditions are analyzed in detail, showing that violations of the null and weak energy conditions are unavoidable but remain localized near the wormhole throat. The anisotropy parameter is positive throughout the spacetime, indicating that repulsive anisotropic stresses play a key role in sustaining the wormhole. The equilibrium configuration is examined using the generalized Tolman-Oppenheimer-Volkoff (TOV) equation for both zero and logarithmic redshift functions, where a consistent force balance is achieved with anisotropic effects providing the dominant outward support. Dynamical stability is studied through scalar perturbations, leading to a Schr\"odinger-like wave equation with a single-peak effective potential. The quasinormal modes are computed using the sixth-order WKB method with Pad\'e approximation. The resulting frequencies possess negative imaginary parts, indicating stable damping of perturbations. Time-domain simulations further confirm the stability of the solutions and show good agreement with the WKB results, with small deviations in the damping rates. Thus, these results establish that $f(Q)$ gravity admits traversable wormhole solutions that are geometrically consistent and dynamically stable, with $f(Q)$ gravity effects effectively regulating the required matter content.

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gr-qc 2026-05-11 2 theorems

CSS laser link tests gravitational redshift to 5×10^{-7}

Formulation of testing gravitational redshift based on Laser Time link between China Space Station and a ground station

Simulations using real orbit data improve prior precision by an order of magnitude and support 0.1 m²/s² potential difference measurements.

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This paper presents a high-precision gravitational redshift test using the China Space Station (CSS) Laser Time Transfer (CLT) system. We develop a comprehensive observation equation based on a c^{-3} order relativistic model for space-ground clock comparison. While the CSS optical clock system is currently in the orbital debugging phase, our simulation using actual CSS orbit data achieves a gravitational redshift verification precision of (1.8 \pm 47)*10^{-7} -- approximately one order of magnitude improvement over previous experiments. Our work represents the first application of laser-based time transfer for gravitational redshift verification at such precision, and the first use of the CSS CLT link for testing this fundamental aspect of General Relativity. Unlike microwave-based methods, our laser approach avoids ionospheric effects and first-order Doppler shifts. Residual analysis identifies tropospheric delay variations and atmospheric turbulence as the primary remaining uncertainty contributors. The achieved precision enables gravitational potential difference measurements with 0.1 m^2/s^2 precision -- offering new capabilities for both fundamental physics investigations and geodetic applications including intercontinental height transfer. This work establishes a new benchmark for high-precision tests of relativistic physics and demonstrates the transformative potential of space-based optical time transfer.

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gr-qc 2026-05-11 3 theorems

Quantum corrections boost gravitational wave signals from black hole orbits

Probing Gravitational Wave Signatures from Periodic Orbits of Regular Black Holes in Asymptotically Safe Gravity

As the scaling parameter rises, amplitude modulations and peak strains increase in the millihertz band accessible to LISA, Taiji, and TianQ

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We investigate bound and periodic timelike geodesics and their associated gravitational-wave (GW) signatures in the spacetime of a regular black hole arising in asymptotically safe gravity (ASG). The geometry incorporates quantum corrections via a running gravitational coupling, encoded in a dimensional scaling parameter $\xi$, that modifies the near-horizon structure while preserving asymptotic flatness. We derive the effective potential for massive test particles and determine the conditions for stable circular and bound motion as functions of $\xi$, including the shift in the innermost stable circular orbit (ISCO). The three topological integers $(z,w,v)$, which represent the number of zooms, whirls, and vertices per radial cycle, are used to categorize the test particles' periodic orbits using Levin's zoom -- whirl taxonomy. Moreover, we employ the rational frequency ratio $q = \frac{\omega_\phi}{\omega_r} - 1$ to find closed orbits, where $\omega_\phi$ and $\omega_r$ stand for the azimuthal and radial frequencies, respectively. We examine how the orbital frequency spectrum is altered, whirl behaviour is enhanced, and deviations from the Schwarzschild limit are produced by the quantum parameter $\xi$. The GW forms for extreme mass-ratio inspirals (EMRIs) are calculated within the quadrupole approximation. We find that as $\xi$ increases, the signals that are released exhibit detectable amplitude modulations and phase shifts. The corresponding typical strain spectra fall within the anticipated sensitivity limits of space-based detectors such as LISA, Taiji, and TianQin, as they peak in the millihertz frequency band. Peak strain increases monotonically with $\xi$, indicating that observational restrictions on quantum-gravity-induced deviations from classical general relativity in the strong-field domain can be obtained from precise measurements of zoom -- whirl dynamics in EMRIs.

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gr-qc 2026-05-08 2 theorems

Causal-set ladders mark black-hole horizons via discrete expansion flip

Towards black-hole horizons and geodesic focusing in causal sets

In a 1+1D toy model, a sign change in geodesic expansion locates the horizon and enables explicit construction of a discrete horizon portion

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The event horizon of a black hole is arguably the most dramatic manifestation of the fact that in General Relativity, causal structure is dynamical and spacetimes can be separated into distinct regions by causal boundaries. Causal set quantum gravity is an approach to quantum gravity in which causal relations between spacetime points constitute the basic structure on which the theory is based. This raises the question how a discrete horizon can be identified in a causal set. In our paper, we first construct a local diagnostic to approximate a global concept, namely the event horizon, based on discrete timelike curves. We then turn to the concept of an apparent horizon, which is based on local properties of geodesics, rather than global properties of the entire spacetime. We undertake first steps towards detecting apparent horizons in causal sets, using so-called ladders as tracers of null geodesics. We find that a discrete counterpart of the expansion changes sign across the black-hole horizon, as it should. Finally, we introduce the notion of a fuzzy ladder, which enables us to track null geodesics for larger intervals of the affine parameter. Thereby, we construct a portion of a discrete horizon in a toy-model for a black-hole spacetime in 1+1 dimensions.

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gr-qc 2026-05-08

Curvature singularities locate black-hole phase transitions

Quasi-homogeneous black hole geometrothermodynamics in Einstein-Maxwell theory

GTD metrics for Reissner-Nordstrom, Kerr and Kerr-Newman solutions place singularities at the same points as heat-capacity divergences.

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In this review, we establish the mathematical framework of geometrothermodynamics (GTD) as a formalism capable of describing non-extensive, quasi-homogeneous, self-gravitating systems in a Legendre-invariant manner. We argue that the fundamental equations of black holes are quasi-homogeneous functions, a property that invalidates the standard Euler identity of laboratory thermodynamics. We derive the metrics for the equilibrium manifold and analyze their curvature singularities for the Reissner-Nordstr\"om, Kerr, and Kerr-Newman black holes. Furthermore, we establish a direct correspondence between the curvature singularities of the equilibrium space and phase transitions, as determined by the divergences of the corresponding heat capacities.

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gr-qc 2026-05-08

Axial modes in anisotropic neutron stars obey universal quadratic law

On the non-radial oscillations of realistic anisotropic neutron stars: Axial modes

Mass-scaled frequency and damping time depend quadratically on compactness and are largely independent of equation of state or anisotropy

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Non-radial oscillation modes of neutron stars serve as diagnostics of their internal composition and relativistic structure. In this work, we investigate the perturbations of static and spherically symmetric neutron stars characterized by an anisotropic pressure. Given the background symmetry, perturbations decouple into polar and axial modes. To date, axial modes have remained less explored, primarily because matter and metric perturbations decouple in the isotropic limit. In this work, we provide a consistent treatment of axial modes and demonstrate that pressure anisotropy induces a direct coupling between matter and metric perturbations. We employ parameterized anisotropy models that ensure consistency with the treatment of matter perturbations. We numerically integrate the linearized Einstein field equations for the axial modes, employing a diverse set of realistic equations of state. Our results indicate that as the stellar mass grows, the frequency of the lower $w$-mode generally decreases, while its damping time increases. Softer equation of states typically yield slightly higher oscillation frequencies. Furthermore, larger anisotropy (i.e., when the tangential pressure exceeds the radial pressure) allows for more massive equilibrium configurations, which correspondingly leads to lower oscillation frequencies and prolonged damping times. Finally, we demonstrate that the frequency and damping time, both scaled by the stellar mass, exhibit a nearly universal quadratic dependence on the stellar compactness, remaining largely insensitive to both the underlying equation of state and the specific anisotropy model.

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gr-qc 2026-05-08

Nonrelativistic gravity yields spin-quadrupole solutions up to NNLO

Spin and Quadrupole Sectors in Nonrelativistic Gravity

The large-c ADM expansion gives consistent Galilean weak-branch metrics with mixed corrections and strong-branch Kerr data through next-to-n

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We study the large-$c$ expansion of general relativity in ADM variables. Using a unified even $\omega$-expansion, the ADM formulation gives a common starting point for Galilean and Carrollian limits. We focus on the Galilean branch and derive the ADM action and field equations up to NNLO. We then construct stationary vacuum solutions in weak and strong branches. In the weak branch, we find NLO Kerr-type, Hartle-Thorne-type and mixed-type solutions. The NLO weak equations also allow a simple extension to higher mass multipoles. At NNLO, the weak Kerr-type and extended Hartle-Thorne-type sectors solve the equations separately, but their naive sum is not a solution. The nonlinear NNLO equations generate mixed $J^2Q$ source terms, which require additional corrections to the NNLO lapse and NNLO spatial tensor field. This gives a mixed weak-branch Galilean solution in the ADM gauge. In the strong branch, Kerr-type data solve the equations through NNLO while the strong Hartle-Thorne-type data solve the NLO equations. We also explain how the ADM data can be reconstructed into approximate spacetime metrics. Since these metrics include spin, quadrupole and mixed spin-quadrupole effects, they may be useful for studying the spacetime around rotating compact objects such as black holes and neutron stars.

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gr-qc 2026-05-08

Non-canonical Brans-Dicke theory matches ΛCDM background evolution

Cosmological Dynamics of a Non-Canonical Generalised Brans-Dicke Theory

Dynamical systems analysis finds stable critical points for constant, power-law and exponential potentials that reproduce key ΛCDM features.

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The LCDM model has been presented with a number of cosmic tensions in the face of precision cosmological data, suggesting the presence of a dynamical dark energy component. In this context, we investigate the cosmology arising from a generalisation of Brans-Dicke theory, with a non-minimally coupled scalar field characterising deviations from standard general relativity, and having a non-canonical kinetic term. By reformulating the field equations into an autonomous set of dynamical equations, we use the methods of dynamical systems to investigate the equilibrium states of the system and their stability for a set of widely-used potentials, namely the constant, power-law, and exponential potentials, with the flow visualized using bounded phase portraits. Furthermore, we investigate the physical meaning of the critical points, and we find viable solutions that can reproduce the characteristics of the $\Lambda$CDM model at background level for each of the three potentials. Furthermore, in each case, we observe that the dynamical behaviour differs noticeably from that observed in other scalar-tensor models due to the non-minimal coupling and non-canonical field, despite using similarly defined dynamical variables.

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gr-qc 2026-05-08

Relational clock erases zero-volume singularity

Singularity Resolution in Quantum Cosmology via Page-Wootters Formalism

Conditional probabilities in a quantum Bianchi universe drop to zero at vanishing volume for every clock reading.

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We investigate the problem of classical big bang singularity in a plane-symmetric Bianchi type-I universe within the Wheeler-DeWitt (WDW) framework of quantum gravity. To address the problem of time, we employ the Page-Wootters formalism, which provides a relational notion of dynamics by conditioning the global state on a clock subsystem. Using Misner variables, the WDW equation assumes a Klein-Gordon (KG) type form. Its general solution is constructed as a Gaussian superposition of momentum eigenstates, resulting in an entangled global state between the clock and the remaining subsystem. Within this relational framework, we construct conditional states and obtain the corresponding probability density consistent with the KG-type inner product. The resulting conditional probability density vanishes in the limit of zero volume for all clock values, indicating quantum resolution of the classical singularity. We further show that positivity of the probability density imposes constraints on the admissible clock values, which depend on the parameters of the Gaussian wavepacket. These results highlight the essential role of quantum correlations in the emergence of relational dynamics, and demonstrate that the Page-Wootters formalism provides a consistent and nonsingular probabilistic description of quantum cosmology.

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gr-qc 2026-05-08

Multispinor formalism derives Teukolsky equation for 6D Kerr black holes

Quasi-normal modes of a multi-dimensional rotating Kerr black hole

Extending spinor techniques beyond four dimensions enables quasi-normal mode calculations for gravitational perturbations in higher-D spacet

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The aim of this paper is to present a general way to calculate quasi-normal modes (QNM) of the Teukolsky equation for higher dimensional (d > 4) Kerr spacetime with compactified extra dimensions. In order to do so, we develop a formalism derived from spinors: we call it multispinor formalism. It is based on vectors of two-spinors and permits us to develop a formalism analogous to that of Newman-Penrose in 4d. From this we show how to derive the Teukolsky equation for gravitational perturbations and calculate the QNM. In order to keep calculations simple we fix, as an example, the dimension number to be six, but the work can be readily generalized to other spacetime dimensions.

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gr-qc 2026-05-08

General relativity recast with conformal geometry and dissipation

Classical General Relativity as a Non-Conservative Action-Dependent Field Theory

Removing the scale factor requires a dissipative sector that renders the second-order dynamics non-conservative.

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Scaling symmetries have previously been examined for classical field theories described by singular Lagrangians; in this article, we apply these results to the first-order formulation of General Relativity. It is shown that the dynamical content of the Hilbert action may be formulated in terms of the conformal spacetime geometry, together with a dissipative sector, which is required in order to compensate the elimination of the notion of scale encoded by the conformal factor. Further, we consider the linearisation of the equations of motion of the scale-invariant action, demonstrating that the first-order metric perturbations satisfy a free wave equation, as expected. The second-order dynamics, describing gravitational backreaction, are found to be sourced by quadratic combinations of the first-order perturbations. However, these dynamics are non-conservative, as is made manifest by the presence of terms which couple the action sector with the geometrical degrees of freedom.

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gr-qc 2026-05-08

Scalar reconstruction yields viable late-time acceleration in HL cosmology

Scalar-Field Reconstruction of Ricci--Gauss--Bonnet Dark Energy in Hov{r}ava--Lifshitz Cosmology

The model produces an equation of state that approaches negative one, keeps sound speed positive, and satisfies the generalized second law.

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This paper reports a Ricci-Gauss-Bonnet (RGB) dark energy model within the framework of Ho\v{r}ava-Lifshitz cosmology and presents a scalar-field reconstruction of the effective dark energy sector. In a spatially flat FRW background with a power-law scale factor, we derive analytical expressions for cosmological parameters, scalar field kinetic term, and the reconstructed potential. The reconstructed EoS parameter exhibits smooth transition toward a cosmological-constant-like regime at late times for suitable choices of the model parameters. The classical stability of the model is analyzed through the squared sound speed, and stable regions of the parameter space are identified. Finally, the generalized second law of thermodynamics is investigated at the apparent horizon, and it is shown that the total entropy variation remains non-negative in this model. From these results it can be concluded that the model provides a theoretically consistent description of late-time acceleration, with physical viability maintained within a specific range of the model parameters.

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gr-qc 2026-05-08

Cored NFW dark matter enlarges black hole photon rings

Adaptive ray tracing, image diagnostics, and photon ring signatures of rotating dark-matter-dressed black holes

Ray tracing shows cored-NFW halos around spinning black holes yield larger apparent images and clearer deviations than Einasto halos or pure

abstract click to expand

We study the optical appearance of rotating black holes embedded in dark matter environments using a phenomenological ray tracing framework. Rather than focusing on a single geometry, we compare two effective rotating backgrounds obtained from static dark matter sourced seed metrics: a regular Einasto-type black hole and a cored-NFW black hole. Kerr is used as the reference spacetime. We construct observer-screen images by numerical backward ray tracing and analyse the horizon structure, shadow boundary, lensing bands, transfer maps, and synthetic intensity distributions produced by a common semi-analytic accretion prescription. We also introduce simple image-level diagnostics, an angular-size confrontation with M87* and Sgr A*, and simplified visibility-amplitude diagnostics. These additions are not intended as an EHT fit, but as a controlled way to identify which observables are most affected by the dark matter dressing. For the representative parameters considered here, the Einasto-supported geometry remains very close to Kerr, while the cored-NFW case produces a stronger redistribution of the image, with larger centroid displacement, stronger brightness asymmetry, an outward shift of the characteristic bright-ring scale, and a visible change in the normalized visibility amplitude. The results indicate that rotating dark-matter-dressed backgrounds can produce systematic image-domain and Fourier-domain deviations that are partially degenerate with spin, inclination, and emission modelling. The framework is lightweight and extensible, and provides a first step toward future GRRT and GRMHD studies of rotating black holes in dark matter environments.

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gr-qc 2026-05-08 2 theorems

Dark matter shifts black hole photon rings outward

Adaptive ray tracing, image diagnostics, and photon ring signatures of rotating dark-matter-dressed black holes

Cored NFW models produce larger centroid displacement and ring-scale changes than Einasto models in ray-traced images.

abstract click to expand

We study the optical appearance of rotating black holes embedded in dark matter environments using a phenomenological ray tracing framework. Rather than focusing on a single geometry, we compare two effective rotating backgrounds obtained from static dark matter sourced seed metrics: a regular Einasto-type black hole and a cored-NFW black hole. Kerr is used as the reference spacetime. We construct observer-screen images by numerical backward ray tracing and analyse the horizon structure, shadow boundary, lensing bands, transfer maps, and synthetic intensity distributions produced by a common semi-analytic accretion prescription. We also introduce simple image-level diagnostics, an angular-size confrontation with M87* and Sgr A*, and simplified visibility-amplitude diagnostics. These additions are not intended as an EHT fit, but as a controlled way to identify which observables are most affected by the dark matter dressing. For the representative parameters considered here, the Einasto-supported geometry remains very close to Kerr, while the cored-NFW case produces a stronger redistribution of the image, with larger centroid displacement, stronger brightness asymmetry, an outward shift of the characteristic bright-ring scale, and a visible change in the normalized visibility amplitude. The results indicate that rotating dark-matter-dressed backgrounds can produce systematic image-domain and Fourier-domain deviations that are partially degenerate with spin, inclination, and emission modelling. The framework is lightweight and extensible, and provides a first step toward future GRRT and GRMHD studies of rotating black holes in dark matter environments.

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gr-qc 2026-05-08 Recognition

Black hole field equations give thermodynamics without constraints

A Constraint-Free Formulation of Black Hole Thermodynamics from the Field Equations

Evaluating the Einstein equations at the outer horizon for general changes in mass, spin and charge directly produces the first law

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We develop a constraint-free formulation that generalizes Padmanabhan's method for deriving the first law of black hole thermodynamics directly from the Einstein field equations. In previous studies, even for multi-horizon black holes, variations were restricted to the outer horizon by imposing an additional constraint, and the PdV term was introduced by multiplying the field equations evaluated at the outer horizon by the corresponding volume variation dV. However, since general variations of the black hole parameters shift both horizons, variations at both horizons must be taken into account. To this end, we propose multiplying the horizon field equations by the entropy variation dS under such unconstrained variations. We show that this method remains valid even in higher-derivative theories of gravity. In addition, we find that $r_{\pm}$-based variation schemes generically break down for black holes characterized by three independent parameters (M,J,Q). By working directly in the thermodynamic state space (M,J,Q), we show that the Einstein field equations evaluated at the outer horizon can be also interpreted as the first law of black hole thermodynamics for general variations without imposing any additional constraints.

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gr-qc 2026-05-08

LISA distinguishes eccentric from circular black hole binaries in stochastic signal

Implications of the LISA stochastic signal from eccentric stellar mass black hole binaries in vacuum

High initial eccentricities at 10^{-4} Hz produce a background separable by Bayesian analysis, while thermal cases depend on formation and a

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Astrophysical formation channels of stellar-mass binary black holes (sBBHs) can induce significant orbital eccentricities in their early inspiral. We analyze the implications on the stochastic gravitational-wave background (SGWB) from unresolved sBBHs, which can be detected with the Laser Interferometer Space Antenna (LISA). We develop an improved SGWB model for the case of an idealized Dirac-delta eccentricity distribution, and extend it to the more astrophysical case of a thermal distribution. Using a fully Bayesian framework, we find that, if all binaries have a high initial eccentricity $e_0 \gtrsim 0.9$ at an orbital frequency of $f_{\rm orb} = 10^{-4}\,\mathrm{Hz}$, the resulting SGWB can be robustly distinguished from a background of quasi-circular sBBHs. For a thermal eccentricity distribution, the SGWB is consistent with a circular model when binaries form at $f_{\rm orb} = 10^{-5}\,\mathrm{Hz}$, but leads to significant systematic biases if formation occurs at $f_{\rm orb} = 10^{-4}\,\mathrm{Hz}$. We also show that, when eccentricity is properly accounted for, environmental effects such as dynamical friction can be distinguished from vacuum evolution, but only for sufficiently dense environments with gas densities $\rho \gtrsim 10^{-7}\,\mathrm{g\,cm^{-3}}$. Finally, we show that a LISA detection of the sBBH SGWB would place an upper bound on the maximum eccentricity of the sBBH population in the band of ground-based detectors, with direct implications for template modeling and data analysis. Our results highlight the importance of incorporating eccentricity in SGWB modeling to enable accurate astrophysical interpretation of LISA observations.

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gr-qc 2026-05-07

Individual black hole pairs let pulsar arrays probe gravity beyond Einstein

Testing General Relativity with Individual Supermassive Black Hole Binaries

Nanohertz signals from supermassive pairs carry phase information that can reveal departures from general relativity over cosmic distances.

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We develop a unified framework for testing gravity beyond General Relativity (GR) with continuous gravitational waves (CWs) from individual supermassive black hole binaries (SMBHBs). These long-lived, nearly monochromatic nanohertz signals offer unique strengths for precision tests of gravity, since their coherent phase evolution and inter-pulsar correlations in pulsar timing arrays (PTAs) retain detailed information about departures from GR over cosmological propagation distances. We consider three representative classes of deviations from GR: additional polarization states, modified dispersion relations, and parity-violating birefringence. For each, we derive the inter-pulsar cross correlation, the modified antenna response, and the propagation-induced pulsar-term phase delay. For non-tensorial polarizations, the CW cross correlation scales linearly in the alternative-polarization amplitude, compared to the quadratic scaling of the gravitational-wave background (GWB), provided the beyond-GR modes are sub-dominant. PTAs are also competitive for modified dispersion relations, where low frequencies enhance both the antenna-pattern modification and the pulsar-term phase delay. Birefringence, by contrast, is suppressed at nanohertz frequencies for most parity-violating theories. We validate the framework with injection-and-recovery simulations for breathing-mode and massive-graviton signals at current observational limits, recovering the injected beyond-GR parameters and distinguishing the CW signal from both correlated and uncorrelated background models. We further show that a pure-GR CW template recovers source parameters without significant bias when beyond-GR physics is present in the data, supporting a two-stage analysis strategy: identify candidates under GR, then test for deviations.

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gr-qc 2026-05-07

Two-parameter vacuum solution found for New General Relativity

Exact solution and Classical tests of New General Relativity

Classical tests tighten the allowed range of the extra parameter beyond earlier limits.

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In this work, we present an exact static spherically symmetric vacuum solution of the New General Relativity (NGR) field equations. Unlike the Schwarzschild solution in General Relativity (GR), this solution is characterized by two parameters. Subsequently, using the four classical tests of relativistic gravity (perihelion precession, light bending, Shapiro time delay and gravitational redshift), a more stringent constraint on the value of the second parameter was derived compared to the original work [1].

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gr-qc 2026-05-07

LISA constrains bumblebee gravity parameter to 10^{-4} with EMRIs

Constraining Lorentz symmetry breaking in bumblebee gravity with extreme mass-ratio inspirals

Modified orbital frequencies in the Lorentz-violating spacetime produce measurable phase shifts in long-lived EMRI signals.

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Extreme mass-ratio inspirals (EMRIs), with their long-lived and highly relativistic orbital evolution, can probe strong-field spacetime geometry and provide an important means to test general relativity. In this work, we investigate EMRI waveforms in a Schwarzschild-like black hole spacetime arising in bumblebee gravity, where Lorentz symmetry breaking (LSB) is characterized by a dimensionless parameter $\ell$. We construct EMRI waveforms within the Augmented Analytic Kludge (AAK) framework using the modified orbital frequencies and fluxes. We find that $\ell$ significantly affects the orbital evolution and thereby modifies the waveform. These modifications grow with increasing $\ell$ and are further enhanced for more eccentric orbits. Furthermore, using Bayesian analysis, we obtain the posterior distributions of EMRI with the parameter $\ell$ included. Our results show that all injected source parameters are recovered within their $1\,\sigma$ credible intervals. We find that the bumblebee parameter $\ell$ can be constrained with an uncertainty of order $\mathcal{O}(10^{-4})$ by LISA.

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gr-qc 2026-05-07 2 theorems

LISA could bound bumblebee gravity ell to 10 to the minus 4

Constraining Lorentz symmetry breaking in bumblebee gravity with extreme mass-ratio inspirals

Extreme mass-ratio inspirals accumulate measurable phase shifts from the Lorentz-breaking parameter in long-lived orbits.

abstract click to expand

Extreme mass-ratio inspirals (EMRIs), with their long-lived and highly relativistic orbital evolution, can probe strong-field spacetime geometry and provide an important means to test general relativity. In this work, we investigate EMRI waveforms in a Schwarzschild-like black hole spacetime arising in bumblebee gravity, where Lorentz symmetry breaking (LSB) is characterized by a dimensionless parameter $\ell$. We construct EMRI waveforms within the Augmented Analytic Kludge (AAK) framework using the modified orbital frequencies and fluxes. We find that $\ell$ significantly affects the orbital evolution and thereby modifies the waveform. These modifications grow with increasing $\ell$ and are further enhanced for more eccentric orbits. Furthermore, using Bayesian analysis, we obtain the posterior distributions of EMRI with the parameter $\ell$ included. Our results show that all injected source parameters are recovered within their $1\,\sigma$ credible intervals. We find that the bumblebee parameter $\ell$ can be constrained with an uncertainty of order $\mathcal{O}(10^{-4})$ by LISA.

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gr-qc 2026-05-07

Wormhole ringdown damping tracks galactic compactness

Perturbations in the parametrized wormhole spacetime and their related quasinormal modes

Shadow bounds on Sgr A* yield viable parameters where decay rates vary with compactness while oscillation frequencies stay stable.

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We study electromagnetic perturbations and the associated quasinormal modes (QNMs) of parametrized static, spherically symmetric wormhole spacetimes, focusing on Damour-Solodukhin and braneworld geometries as well as their galactic extensions. Using the Bronnikov-Konoplya-Pappas parametrization, we express the metric functions in terms of a compactified radial coordinate and characterize the spacetime through far-field and near-throat parameters. The far-field coefficients govern the asymptotic structure and post-Newtonian behaviour, while the near-throat continued-fraction expansion captures the strong-field geometry near the throat. We first apply the parametrization to isolated wormholes and identify its range of validity, showing that non-polynomial metric functions can limit the convergence of the near-throat expansion and hence the accuracy of a truncated representation. We then extend the framework to a galactic Damour-Solodukhin wormhole embedded in a Hernquist dark matter halo. Imposing observational bounds from the shadow of Sgr A$^*$, we constrain the galactic compactness and deformation parameters and obtain an observationally viable parametrized metric. Within the allowed parameter space, we compute the fundamental QNM frequencies using the transfer matrix method and analyze the corresponding time-domain ringdown signals. We find that the damping rate is more sensitive to galactic compactness, whereas the oscillation frequency remains comparatively stable. Although the spectral shifts are small within the shadow-allowed region, the framework provides a systematic link between geometric parametrization, shadow constraints, and dynamical response. Our results establish an observationally consistent parametrized description of wormhole perturbations for strong-field tests of horizonless compact objects.

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gr-qc 2026-05-07 Recognition

Consistent minisuperspace quantizations solved for black holes and universes

Canonical quantization of all minisuperspaces with consistent symmetry reductions

Hamiltonian and conformal symmetries promoted to operators yield Wheeler-DeWitt solutions across Schwarzschild, FLRW and Bianchi geometries.

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We present the quantization of all symmetry reductions of the Einstein--Hilbert Lagrangian that correctly reproduce the reduced Einstein's field equations -- i.e., characterized by the infinitesimal group actions obeying the principle of symmetric criticality. These correspond to the spacetime symmetries of spherical/hyperbolic/planar Schwarzschild/Taub--NUT, BI/BII/BIII-metrics, near-horizon extreme Kerr geometry, swirling universe, closed/open/flat FLRW cosmologies, other FLRW-type metrics, and Bianchi type I, II, VIII, and IX spacetimes. We derive the Hamiltonian and the conformal symmetries of the superspace metrics (the conditional symmetries), promote them to operators, and solve the Wheeler--DeWitt equation with and without imposing these symmetries.

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gr-qc 2026-05-07

All consistent minisuperspaces admit canonical quantization

Canonical quantization of all minisuperspaces with consistent symmetry reductions

Superspace conformal symmetries are promoted to operators and the Wheeler-DeWitt equation is solved for Schwarzschild, Bianchi and FLRW-type

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We present the quantization of all symmetry reductions of the Einstein--Hilbert Lagrangian that correctly reproduce the reduced Einstein's field equations -- i.e., characterized by the infinitesimal group actions obeying the principle of symmetric criticality. These correspond to the spacetime symmetries of spherical/hyperbolic/planar Schwarzschild/Taub--NUT, BI/BII/BIII-metrics, near-horizon extreme Kerr geometry, swirling universe, closed/open/flat FLRW cosmologies, other FLRW-type metrics, and Bianchi type I, II, VIII, and IX spacetimes. We derive the Hamiltonian and the conformal symmetries of the superspace metrics (the conditional symmetries), promote them to operators, and solve the Wheeler--DeWitt equation with and without imposing these symmetries.

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gr-qc 2026-05-07

Matter cat state displaces graviton vacuum into coherent states

Quantum gravitational contrast in creating Schr\"odinger cat state

Their overlap defines a gravitational contrast that measures how distinct the quantum geometries are for each superposition branch.

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In this paper, we illustrate how a Schr\"odinger cat state created via a matter-wave interferometer can be viewed as the simplest quantum-gravity setup where we can treat both matter and gravity on an equal footing at a perturbative level. Here we treat Einstein's theory of general relativity using an effective field theory approach, quantising the massless spin-2 graviton in the presence of a quantum spatial superposition of matter that creates a matter-wave interferometer in the non-relativistic limit. We show that due to the matter-graviton coupling the graviton vacuum is displaced analogous to the coherent state. We study the contrast/overlap between the coherent states of the left and right superpositions in the matter-wave interferometer. We also study the entanglement between matter and the graviton in this setup and relate it to a gravitational contrast, or the overlap of the quantum geometries led by the coherent states. In the appendix, we provide an example of a time-dependent harmonic oscillator and study the contrast/overlap of such coherent states of the graviton.

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gr-qc 2026-05-07

Exact AdS black hole with Kalb-Ramond field shows phase transitions

Extended thermodynamics and P-v Criticality of Kalb-Ramond black hole coupled with nonlinear electrodynamics

The solution produces swallow-tail Gibbs free energy and non-area-law entropy when nonlinear electrodynamics is coupled to the Kalb-Ramond 2

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We present an exact black hole solution in anti-de Sitter (AdS) spacetime with a Kalb-Ramond field coupled to nonlinear electrodynamics (NLED), characterized by mass, magnetic monopole charge, and Lorentz-violating parameters. The geometry admits two horizons (inner and outer) that coalesce into a degenerate horizon at a critical monopole charge. Beyond this critical point, no black hole solutions exist. In the limit of vanishing Lorentz-violating parameters, the solution reduces to the modified Kalb-Ramond and Bardeen black holes, while suitable parameter choices reproduce the Reissner-Nordstr\"om-AdS and Schwarzschild-AdS geometries. We analyze the thermodynamics of the solution by computing the Hawking temperature, entropy, specific heat, and Gibbs free energy. The NLED source introduces nontrivial modifications: the Hawking temperature displays nonmonotonic behavior with possible local extrema, the entropy deviates from the standard area law, and the specific heat may assume negative values, signaling thermodynamic instabilities. The Gibbs free energy exhibits swallow-tail structures, indicative of first-order phase transitions. Furthermore, we derive the first law of black hole thermodynamics in the extended phase space, together with the Smarr relation, and confirm their validity for the Kalb-Ramond black holes with NLED sources. Our findings highlight the rich thermodynamic structure induced by Lorentz-violating effects and nonlinear electrodynamics in AdS black hole backgrounds.

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